Discretize the SDE in the form: x_{i+1} = x_i + f_i(x_i) + G_i z_i. Useful for reverse diffusion sampling and probabiliy flow sampling. Defaults to Euler-Maruyama discretization. Args: x: a torch tensor t: a torch float representing the time step (from 0 to `self.T`) R
(self, x, t)